#include <stdio.h>
int main()
{
	int x = 0;
	float y = 0;
	scanf("%d",&x);
	if(x <1)
	  y = x;
	  else if(x < 10 &&x >= 1)
	    y = 2*x-1;
		else
		  y = 3*x-11;
		  printf("%.2f",y);
	
	return 0;
}
